The present invention relates to an aqueous dispersion for chemical mechanical polishing. More specifically, it relates to an aqueous dispersion for chemical mechanical polishing that is particularly useful for chemical mechanical polishing of insulating films during the manufacturing steps for semiconductor devices.
Improvements in degrees of semiconductor device integration and increased multilayer wiring have led to drastic increases in storage volumes of memory devices. This has been supported by advances in micronization for the working techniques, increased multilayer wiring and the steps for micronization are increasing correspondingly, thus leading to higher chip costs. Given such circumstances, chemical mechanical polishing techniques for polishing of working film and the like been introduced and attention is being directed toward these techniques. Application of such chemical mechanical polishing techniques has allowed planarization and numerous micronization techniques.
One of these micronization techniques is Shallow Trench Isolation, also known as STI. The important factor for the STI technique is the removal rate ratio between the silicon nitride film used as the stopper film and the silicon oxide film, or the xe2x80x9cselectivityxe2x80x9d, and an optimum polishing agent is necessary.
In light of the state of the aforementioned STI technique, it is an object of the present invention to provide an aqueous dispersion for chemical mechanical polishing with a high removal rate for silicon oxide film and a low removal rate for silicon nitride film, i.e. a high selectivity.
The present invention is as follows.
1. An aqueous dispersion for chemical mechanical polishing characterized by comprising an inorganic abrasive and organic particles with anionic group, wherein the removal rate for silicon oxide film is at least 5 times the removal rate for silicon nitride film.
2. An aqueous dispersion for chemical mechanical polishing according to 1. above, wherein the abovementioned anionic group is at least one selected from among carboxyl group, hydroxyl group, sulfuric acid ester group, sulfonic acid group, phosphoric acid group and epoxy group.
3. An aqueous dispersion for chemical mechanical polishing according to 2. above, wherein the abovementioned inorganic abrasive is at least one selected from the group consisting of silica, ceria, alumina, titania and zirconia.
4. An aqueous dispersion for chemical mechanical polishing according to 3. above, wherein the zeta potential of the abovementioned organic particles with the abovementioned anionic group is xe2x88x9210 mV or lower.
5. An aqueous dispersion for chemical mechanical polishing according to 2. above, wherein the abovementioned inorganic abrasive is fumed silica or colloidal silica.
6. An aqueous dispersion for chemical mechanical polishing according to 5. above, wherein the zeta potential of the abovementioned organic particles with the abovementioned anionic group is xe2x88x9210 mV or lower.
7. An aqueous dispersion for chemical mechanical polishing according to 6. above, wherein the zeta potential of the abovementioned organic particles with the abovementioned anionic group is xe2x88x9220 mV or lower.
8. An aqueous dispersion for chemical mechanical polishing according to 7. above, which is used for a shallow trench isolation step in the manufacture of a semiconductor device.
9. An aqueous dispersion for chemical mechanical polishing according to 1. above, which further comprises an anionic surfactant, wherein when the abovementioned inorganic abrasive is silica, the removal rate for silicon oxide film is at least 6 times the removal rate for silicon nitride film.
10. An aqueous dispersion for chemical mechanical polishing according to 9. above, wherein the abovementioned anionic group is at least one selected from among carboxyl group, hydroxyl group, sulfuric acid ester group, sulfonic acid group, phosphoric acid group and epoxy group.
11. An aqueous dispersion for chemical mechanical polishing according to 10. above, wherein the zeta potential of the abovementioned organic particles with the abovementioned anionic group is xe2x88x9210 mV or lower.
12. An aqueous dispersion for chemical mechanical polishing according to 11. above, which is used for a shallow trench isolation step in the manufacture of a semiconductor device.
13. An aqueous dispersion for chemical mechanical polishing according to 1. above, which further comprises an anionic surfactant, wherein when the abovementioned inorganic abrasive is ceria, the removal rate for silicon oxide film is at least 10 times the removal rate for silicon nitride film.
14. An aqueous dispersion for chemical mechanical polishing according to 13. above, wherein the abovementioned anionic group is at least one selected from among carboxyl group, hydroxyl group, sulfuric acid ester group, sulfonic acid group, phosphoric acid group and epoxy group.
15. An aqueous dispersion for chemical mechanical polishing according to 14. above, wherein the zeta potential of the abovementioned organic particles with the abovementioned anionic group is xe2x88x9210 mV or lower.
16. An aqueous dispersion for chemical mechanical polishing according to 15. above, which is used for a shallow trench isolation step in the manufacture of a semiconductor device.
According to the invention, it is possible to obtain an aqueous dispersion for chemical mechanical polishing which is useful for STI steps, to allow polishing of silicon oxide film at an adequate rate while maintaining an adequately high selectivity as the ratio with respect to the removal rate for silicon nitride film, and without producing scratching or dishing.
The aqueous dispersion for chemical mechanical polishing of the invention is characterized by comprising an inorganic abrasive and organic particles with anionic group, wherein the removal rate for silicon oxide film is at least 5 times the removal rate for silicon nitride film.
The xe2x80x9cinorganic abrasivexe2x80x9d may be silica, ceria, alumina, titania, zirconia or the like, and particularly preferred are silica and ceria. The silica used may be (1) fumed silica obtained by reacting silicon chloride in the presence of hydrogen and oxygen, (2) colloidal silica obtained by ion-exchange of a silicic acid salt, or (3) colloidal silica obtained by hydrolysis or condensation of a metal alkoxide. The ceria used may be obtained by firing of cerium carbonate, cerium hydroxide or cerium oxalate, but ceria obtained by firing of cerium carbonate is particularly preferred. The inorganic abrasive used may be of a single type, but combinations of two or more, such as silica and ceria, silica and alumina or ceria and alumina may also be used.
The average particle size of the inorganic abrasive is preferably 0.01-3 xcexcm, because when the average particle size is less than 0.01 xcexcm it is not possible to obtain an aqueous dispersion with an adequately high removal rate. On the other hand, if the average particle size is greater than 3 xcexcm, the inorganic abrasive settles and easily separates, thus making it difficult to achieve a stable aqueous dispersion. The average particle size is more preferably 0.02-1.0 xcexcm, and even more preferably 0.04-0.7 xcexcm. An inorganic abrasive with an average particle size within this range gives a stable aqueous dispersion for chemical mechanical polishing with a high removal rate, and minimal settling or separation of the abrasive. The average particle size can be measured with a dynamic light scattering type measuring instrument, a laser diffusion diffraction type measuring instrument or the like, or it may be measured by observation with a transmission electron microscope. It may also be calculated based on the specific surface area of the powdered inorganic abrasive.
The content of the inorganic abrasive in the aqueous dispersion will depend on the type of inorganic abrasive, but for silica it may be 2-20 parts by weight (hereunder referred to as xe2x80x9cpartsxe2x80x9d), preferably 4-15 parts and more preferably 6-12 parts, with respect to 100 parts of the aqueous dispersion. If the silica content is less than 2 parts, the removal rate is not adequately improved, and if it is more than 20 parts, the stability of the aqueous dispersion tends to be lower, which is undesirable in terms of cost. For ceria, it may be 0.02-5 parts, preferably 0.05-2 parts and more preferably 0.1-1 part with respect to 100 parts of the aqueous dispersion. The ceria content is preferably not below this range or above this range, because the same problems occur as with silica.
The xe2x80x9corganic particlesxe2x80x9d with anionic group may be composed of a resin having anionic group introduced into the molecular chains.
As resin with anionic group introduced into the molecular chains there may be mentioned thermoplastic resin, which include polyvinyl chloride, polystyrene and styrene-based copolymer, polyolefin and polyolefin copolymer such as polyacetal, saturated polyester, polyamide, polycarbonate, polyethylene, polypropylene, poly-l-butene, poly-4-methyl-1-pentene and the like, as well as phenoxy resin, (meth)acrylic resin such as polymethyl methacrylate, and (meth)acrylic copolymer.
There may also be mentioned copolymer resin with crosslinked structures obtained by copolymerization of styrene, methyl methacrylate and the like. with divinylbenzene, ethylene glycol dimethacrylate and the like. There may also be mentioned thermosetting resin such as phenol resin, urea resin, melamine resin, epoxy resin, alkyd resin and unsaturated polyester resin.
The organic particles may be produced by any of various methods including emulsion polymerization, suspension polymerization, emulsified dispersion, pulverization or the like. The organic particles used may be of one type or a combination of two or more types.
The xe2x80x9canionic groupxe2x80x9d may be functional group that can render the zeta potential of the organic particles negative in the aqueous dispersion, and they are not particularly restricted. Specifically, there may be mentioned carboxyl group, hydroxyl group, sulfuric acid ester group, sulfonic group, phosphoric group and epoxy group. Carboxyl group and sulfonic acid group are preferred among these, and carboxyl group is particularly preferred. Organic particles with cationic group result in a relatively lower removal rate for silicon oxide film.
The zeta potential of the organic particles with the anionic group when measured in the water as same pH as the polishing slurry is xe2x88x9210 mV or lower, and preferably xe2x88x9220 mV or lower. The lower limit is normally xe2x88x92100 mV.
The average particle size of the organic particles is preferably 0.01-3 xcexcm. If the average particle size is less than 0.01 xcexcm, the ratio of the removal rate for silicon oxide film with respect to the removal rate for silicon nitride film is reduced, such that the selectivity may not be improved. On the other hand, if the average particle size is greater than 3 xcexcm, the organic particles settle and easily separate, thus making it difficult to achieve a stable aqueous dispersion. The average particle size is more preferably 0.02-1.0 xcexcm, and even more preferably 0.04-0.7 xcexcm. Organic particles with an average particle size within this range result in a stable aqueous dispersion for chemical mechanical polishing with a high selectivity, and minimal settling or separation of the particles. The average particle size can be measured in the same manner as for the inorganic abrasive.
The organic particle content in the aqueous dispersion will depend on the type and the average particle size of the -inorganic abrasive, but in the case of a silica inorganic abrasive it may be 0.05-10 parts, preferably 0.1-5 parts and more preferably 0.2-3 parts, with respect to 100 parts of the aqueous dispersion. If the organic particle content is less than 0.05 part, the selectivity is not adequately improved, and if it is more than 10 parts, the stability of the aqueous dispersion tends to be lower, which is undesirable in terms of cost. In the case of a ceria inorganic abrasive, the organic particle content may be 0.02-5 parts, preferably 0.05-2 parts and more preferably 0.1-1 part with respect to 100 parts of the aqueous dispersion. The organic particle content is preferably not below this range or above this range, because the same problems occur as with a silica inorganic abrasive.
The inorganic abrasive and organic particles do not necessarily need to be dispersed in a mutually independent state. For example, an alkoxysilane may be polycondensed together with the inorganic abrasive and organic particles, with the polysiloxane bonded to at least the surface of the organic particles, and with the inorganic abrasive such as silica or ceria also bonded by electrostatic force. The resulting polysiloxane in this case may be directly bonded to the anionic group of the organic particles, or it may be indirectly bonded through a silane coupling agent or the like.
The medium for the aqueous dispersion may be water or a mixed medium composed mostly of water, such as a mixture of water and methanol, but water alone is particularly preferred.
The aqueous dispersion for chemical mechanical polishing according to the invention comprises an inorganic abrasive, organic particles and water, to provide a polishing agent with high selectivity and excellent performance, which can be used in STI steps for manufacture of semiconductor devices. With conventionally used silica, the selectivity is about 2-3, but according to the invention, the use of a combination of organic particles with anionic group and silica allows a selectivity of 5 or more. When ceria is used as the inorganic abrasive or the conditions are optimized, the selectivity can be increased to 10 or more, 20 or more and even 30 or more.
It is also possible to increase the selectivity by further including an anionic surf actant. For example, when silica is used as the inorganic abrasive, the selectivity can be increased to 6 or more. When ceria is used as the inorganic abrasive, the selectivity can be increased to 10 or more, 20 or more and even 30 or more.
The aqueous dispersion of the invention may also include various additives to further enhance its performance.
By adding an acid it is possible to stabilize the aqueous dispersion, which will further increase the selectivity in some cases. The acid is not particularly restricted, and any organic acid or inorganic acid may be used. As organic acids there may be mentioned para-toluenesulfonic acid, dodecylbenzenesulfonic acid, isoprenesulfonic acid, gluconic acid, lactic acid, citric acid, tartaric acid, malic acid, glycolic acid, malonic acid, formic acid, oxalic acid, succinic acid, fumaric acid, maleic acid, phthalic acid and the like. As inorganic acids there may be mentioned nitric acid, hydrochloric acid, sulfuric acid and the like. These organic acids or inorganic acids may be used alone or in combinations of two or more, and organic acids and inorganic acids may also be used together. These acids may be included at 0.02-2 parts and especially 0.05-1 part with respect to 100 parts of the aqueous dispersion.
A base may also be included in the aqueous dispersion for adjustment of the pH to further enhance the dispersability, removal rate and selectivity. The pH is not particularly restricted but will normally be about 5-12 and preferably 6-11. The base is also not particularly restricted, and any organic or inorganic base may be used. As organic bases there may be mentioned nitrogen-containing organic compounds such as ethylenediamine, ethanolamine and the like. As inorganic bases there may be mentioned ammonia, potassium hydroxide, sodium hydroxide, lithium hydroxide and the like, and these bases may be used alone or in combinations of two or more. The content of these bases is important for adjustment of the pH, but they may be added at 0.01-1 part and especially 0.02-0.5 part with respect to 100 parts of the aqueous dispersion. The preferred pH will differ depending on the inorganic abrasive, and in the case of silica the pH is preferably 10-12, while in the case of ceria the pH is preferably 5-12; these pH ranges are preferred to allow both enhanced removal rate and selectivity.
The aqueous dispersion may also contain, as additional additives, oxidizing agents, polyvalent metal ions, surfactants and the like.
As oxidizing agents, hydrogen peroxide, peroxosulfate, heteropolyacid and the like can be used. As polyvalent metal ions, alminium, titan, chromium, vanadium and the like can be used.
The surfactants may be anionic surfactant, nonionic surfactant, cationic surfactant or amphoteric surfactant, but anionic surfactant are preferred. As examples of anionic surfactant there may be mentioned potassium dodecylbenzene sulfonate, ammonium dodecyl sulfate and the like. The contents of these anionic surfactant may be 0 to 0.5 wt %, preferably 0.005 to 0.2 wt % and more preferably 0.01 to 0.1 wt % with respect to the aqueous dispersion.
There may also be added dispersing agents such as polyacrylic acid and viscosity adjustors such as polyacrylamide.
In the aqueous dispersion of the invention, the aforementioned additives are combined with the inorganic abrasive and the organic particles with anionic group as necessary, to allow further enhancement of the selectivity in STI steps.
When an aqueous dispersion for chemical mechanical polishing according to the invention is used for chemical mechanical polishing of a polishing surface, the polishing may be carried out under prescribed conditions using a commercially available chemical mechanical polishing apparatus (for example, Model xe2x80x9cEPO-112xe2x80x9d and xe2x80x9cEPO-222xe2x80x9d by Ebara Corporation, Model xe2x80x9cLGP510xe2x80x9d or xe2x80x9cLGP552xe2x80x9d by Lapmaster SFT Co., Ltd.; Article name xe2x80x9cMirraxe2x80x9d by Applied Materials Corp.; Article name xe2x80x9cTeresxe2x80x9d by Lam Research Corp. and Model xe2x80x9cAVANTI 472xe2x80x9d by Speed Fam-IPEC Corp.).
The present invention will now be explained in further detail by way of examples.
(1) Synthesis of Organic Particles